The monitor in Heimdall's lab indicates green dots as life signs for a human and orange dots for a Goa'uld symbiote. When O'Neill and Teal'c are imprisoned by the Goa'uld, Teal'c is sitting closest to the door and O'Neill is lying down farthest from the door. The display in Heimdall's lab shows O'Neill (green dot) closest to the door.
After Osiris orders the use of gas to eliminate Teal'c and Jack O'Neill, you see them walking down a corridor. Carter can be seen crouching on the right hand side of the corridor, waiting to pop up as a hologram.
When at the shield generator room door, Carter, as a hologram, casts a shadow.